1. Field of the Invention
This invention relates to electrically conducting fibers impregnated with copper sulfide and to methods of making them.
2. Description of the Prior Art
Numerous methods for imparting electrical conductivity to synthetic polymeric fibers are known in the art. For example, one method for imparting electrical conductivity to polymeric fibers involves plating the surface of the fiber. However, this method requires etching of the surface of the fiber prior to plating so as to obtain satisfactory adhesion. The process also involves sensitizing and activating the fiber prior to plating. In addition, the resulting electrically conducting fiber differs greatly from the starting fiber in softness, flexibility, and smoothness.
In another prior art process, metal is kneaded into a polymer. The polymer is then spun into a yarn. However, this process is plagued by problems such as clogging of the nozzle with metallic particles during spinning. In addition, unless the metal content of the fibers is kept relatively low, the electrically conducting fiber obtained by this prior art method has inferior mechanical properties compared to the starting fiber.
In the third prior art process, metallic powder is deposited in the pores of a polymeric fiber. This method usually requires an extraordinarily porous fiber and intricate process steps.
In the U.S. Pat. Nos. 3,014,818 and 4,122,143 electrically conductive products are produced by reducing a copper compound to metallic copper. In U.S. Pat. No. 3,014,818, an electrically conductive fibrous material is produced by soaking the fiber, such as cotton or acrylic fibers, in a bath comprising a reducible salt of nickel, cobalt, copper, or iron. The fiber is then subjected to a reducing treatment to obtain free metal particles which are dispersed through the interior of the fiber. Sodium borohydride and hydroxylamine are disclosed as satisfactory reducing agents. In U.S. Pat. No. 4,122,143, cured products are obtained by reducing copper simultaneously with the curing of a resin. Imparting electrical conductivity to an already existing fiber is not disclosed.
In the above-described prior art processes, electrical conductivity is obtained by the presence of metallic copper in the polymeric material. However, it is well-known that acrylic or acrylic-series fibers, including modacrylic fibers, have a strong affinity for monovalent copper ions. It is believed that this results from coordinate bonding between the cyanic groups in the fiber and the monovalent copper ions. The absorption of monovalent copper ions into acrylic or acrylic-series fibers, including modacrylic fibers, turns the fibers yellowish. However, as determined by measurements of electrical resistance, etc., the fibers do not develop any electrical conduction at all.
In applicants' Japanese application Nos. Sho 53-124,398 and Sho 55-028386 and in their copending U.S. application Ser. No. 183,639, filed Sept. 3, 1980, electrically conducting acrylic fibers or fibers containing acrylic fibers are disclosed. In these applications, applicants take advantage of the strong affinity of the cyanic group for monovalent copper ions to impart electrical conductivity to the acrylic fiber or to acrylic-series fibers, such as modacrylic fibers. The acrylic fiber or acrylic-series fiber is treated to adsorb monovalent copper ions and at the same time, or in a subsequent step, the fiber is treated with a sulfur-containing compound to convert the adsorbed monovalent copper ions into cupric sulfide or cuprous sulfide.
According to the present invention, the strong affinity of the cyanic group for monovalent copper ions is also taken advantage of to impart electrical conductivity to fibers other than the acrylic fibers, and acrylic series fibers, including modacrylic fibers of the above-mentioned applications. The present invention provides electrically conducting synthetic or natural fibers having cyanic groups introduced therein having excellent electrical conducting properties and washability. The present invention also provides a method for making an electrically conductive fiber from a synthetic or natural fiber by introducing cyanic groups into the synthetic or natural fiber and then converting monovalent copper ions which are absorbed by the fiber containing the cyanic groups into cuprous or cupric sulfide.